Ultrasound from a focused ultrasonic transducer can be used to selectively treat regions within the interior of the body. Ultrasonic waves are transmitted as high energy mechanical vibrations. These vibrations induce tissue heating as they are damped, and they can also lead to cavitation. Both tissue heating and cavitation can be used to destroy tissue in a clinical setting. However, heating tissue with ultrasound is easier to control than cavitation. Ultrasonic treatments can be used to ablate tissue and to kill regions of cancer cells selectively. This technique has been applied to the treatment of uterine fibroids, and has reduces the need for hysterectomy procedures.
To selectively treat tissue, a focused ultrasonic transducer can be used to focus the ultra sound on a particular treatment volume. The transducer is typically mounted within a medium, such as degassed water, that is able to transmit ultrasound. Actuators are then used to adjust the position of the ultrasonic transducer and thereby adjust the tissue region that is being treated. U.S. Pat. No. 5,590,653 describes a medical treatment apparatus where the position of an ultrasonic transducer is adjustable and is integrated into a patient table.
Standard medical imaging techniques are commonly used to plan the ultrasound treatment and can also be used to guide the treatment. Magnetic Resonance Imaging (MRI), Computed Tomography y (CT), and ultrasonic imaging have been used for the planning and guiding of ultrasonic treatments. Focused ultrasonic transducers typically have a limited range over which they can be actuated, so the patient must be positioned properly relative to the ultrasonic treatment apparatus. Ultrasound is not able to be transmitted to the body through air, so an ultrasound coupling such as ultrasonic gel, an ultrasonic gel pad, or degassed water is used to transmit the ultrasound from the ultrasonic treatment apparatus to the skin of the patient. Typically a membrane such as Mylar is used to form a boundary between the ultrasonic treatment apparatus and the medium used to conduct ultrasound to the patient.
A problem with current ultrasonic treatment apparatuses is that the Mylar membranes are fragile and that the ultrasound coupling may not form a good path for the ultrasound if the patient is positioned on the coupling more than once. For many treatment procedures, the patient is positioned relative to the treatment apparatus and a medical imaging technique is used to check the orientation of the patient's anatomy relative to the ultrasonic transducer. If the patient is not orientated relative to the ultrasonic transducer properly, he or she will need to be repositioned. This can cause the ultrasound coupling to be damaged. In this case the coupling will need to be replaced, and this typically means that the process of orientating the patient relative to the ultrasonic transducer needs to be started again. Additionally when the patient is positioning himself or herself on the ultrasonic treatment apparatus, the Mylar window can be damaged, or the ultrasonic coupling disturbed.